The hormone angiotensin II has several prominent actions concerning body fluid balance which are mediated by the central nervous system. Among these effects are water intake, secretion of vasopressin, and a pressor effect. One identified site of action of angiotensin II is the subfornical organ. Tissue bordering the optic recess of the third ventricle, and including the organum vasculosum laminae terminalis, may also possess receptors for the hormone. The interrelationships between these receptor loci, in terms of the central effects of angiotensin and in terms of their anatomical interconnections, will be studied. The functional interrelationships between these structures will also be studied. The synergy between the central effects of angiotensin, in the context of the behaving, unanesthetized animal, will be emphasized in these studies.